remove submitBeaconBlock API

[bharath-123]

No description provided.

[JasonVranek]

I think there's a lot of value in keeping submitBeaconBlock. Today highly connected relays assist in broadcasting signed blocks before the attestation deadline which increases the viability/robustness of more geographically isolated proposers. In ePBS, the auction's winning builder would equally be incentivized to help with the propagation. If we remove this endpoint arguably the same geographically isolated proposers would be disadvantaged.